Lesson 2 Plant Responses

Lesson 2 Plant Responses Student Labs and Activities Page Launch Lab 25 Content Vocabulary 26 Lesson Outline 27 MiniLab 29 Content Practice A 30 Content Practice B 31 Math Skills 32 School to Home 33 Key Concept Builders 34 Enrichment 38 Challenge 39 Skill Practice 40 24 Plant Processes and Reproduction

Launch Lab LESSON 2: 15 minutes How do plants respond to stimuli? Photosynthesis in plants requires light energy. How do plants respond to light in their environment? Procedure 1. Read and complete a lab safety form. 2. Choose a pot of young radish seedlings. 3. Place toothpicks parallel to a few of the seedlings in the pot in the direction of growth. 4. Place the pot near a light source, such as a gooseneck lamp or next to a window. The light source should be to one side of the pot, not directly above the plants. 5. Check the position of the seedlings in relation to the toothpicks after 30 minutes. Record your observations in the Data and Observations section below. 6. Observe the seedlings after two or more hours. Record your observations. Data and Observations Think About This 1. What happened to the position of the seedlings after the first 30 minutes? How could you tell? 2. What happened to the position of the seedlings after an hour or two? 3. Key Concept Why do you think the position of the seedlings changed? Plant Processes and Reproduction 25

Content Vocabulary LESSON 2 Plant Responses Directions: On each line, write the term from the word bank that correctly replaces the underlined words in each sentence. NOTE: You may need to change a term to its plural form. photoperiodism plant hormone stimulus tropism 1. Plants may respond to a change in the environment by growing toward it or away from it. 2. Seedlings bending toward light and roots curving away from light are examples of plant growth toward or away from environmental changes. 3. Due to a response to the number of hours of darkness in their environment, carnations only flower in the summer, when the number of daylight hours is greater than the number of hours of darkness. 4. Auxins, ethylene, gibberellins, and cytokinins are substances that act as chemical messengers within plants. 26 Plant Processes and Reproduction

Lesson Outline LESSON 2 Plant Responses A. Stimuli and Plant Responses 1. are any changes in an environment that cause organisms to respond. 2. A plant will respond to by growing toward it. 3. When stimulated by an insect s, the two sides of a Venus flytrap snap shut immediately, trapping the insect inside. B. Environmental Stimuli 1. Plants responses to different environmental stimuli include, touch, and. 2. A(n) is a response that results in plant growth toward or away from a stimulus. 3. The growth of a plant toward or away from light is called a(n). a. Leaves and tend to grow in the direction of light. b. generally grow away from light. 4. The response of a plant to touch is called a(n). a. Structures that respond to touch, called, can wrap around or cling to objects. b. When, the leaves of Mimosa pudica quickly droop or fold up. 5. The response of a plant to gravity is called. a. grow away from gravity. b. Roots grow gravity. 6. Some plants flower in response to the amount of they are exposed to. a. is a plant s response to the number of hours of darkness in its environment. b. Plants that flower when exposed to less than 10 12 hours of darkness are called plants. Plant Processes and Reproduction 27

Lesson Outline continued c. Short-day plants require 12 or more hours of for flowering to begin. d. plants flower when they reach maturity and the environmental conditions are right. C. Chemical Stimuli 1. are substances that act as chemical messengers within plants. 2. Hormones are called because they are usually produced at one part of a plant and affect another part of that plant. 3. generally cause increased plant growth. 4. helps stimulate the ripening of fruit. 5. increase the rate of cell division and cell elongation in stems and leaves. 6. increase the rate of cell division in some plants and slow the aging process of flowers and fruits. D. Summary of Plant Hormones 1. Plants produce many different. 2. Often, two or more plant hormones interact and produce a plant. E. Humans and Plant Responses 1. Humans make plants more using plant hormones. 2. Some crop plants are now easier to because humans understand how they respond to hormones. 28 Plant Processes and Reproduction

MiniLab LESSON 2: 20 minutes When will plants flower? Did you ever think plants could have strategies so that they can germinate, live, grow, reproduce, and continue their species? Photoperiodism is one such strategy. Procedure 1. In your Science Journal, copy the table shown in your textbook to classify plants based on their photoperiodisms. 2. Choose 8 10 pictures of flowers. Record their names in your table. Use the clues on the back of each photo to determine the correct photoperiodism of each plant. Analyze and Conclude 1. Interpret Data Based on your table, which plants would flower during the summer? 2. Explain why some plants flower at the same time every year. 3. Infer what might happen if artificial light was put on short-day plants for an hour or two at night. 4. Key Concept Why would photoperiodism be an important strategy for flowering plants? Plant Processes and Reproduction 29

Content Practice A LESSON 2 Plant Responses Directions: Circle the term or phrase that correctly completes each sentence. 1. Light, touch, or gravity that causes plant growth toward or away from a stimulus is a (chemical hormone, tropism). 2. A plant s tropism to light is called (phototropism, gravitropism). 3. Bending toward the light is a (positive, negative) tropism. 4. If a planter is turned so the plant bends away from the light, the plant will gradually (bend lower, straighten). 5. The plant s stems (will, will not) continue to grow upward if the plant is placed in the dark. 6. Roots that grow (toward, away from) the Sun help anchor the plant in the soil. 7. Some plants respond to touch. This is called (thigmotropism, photoperiodism). 8. A higher level of a plant hormone called (gibberellins, auxin) on the dark side of the plant causes plant cells found there to grow longer. 9. When plant cells on the dark side of a plant grow longer, the plant (bends, dies). 30 Plant Processes and Reproduction

Content Practice B LESSON 2 Plant Responses Directions: On each blank line, write the term from the word bank that correctly completes each sentence. Some terms may be used more than once or not at all. auxins chemical day-neutral environmental ethylene gibberellins gravitropism hormones interact long-day negative photoperiodism productive response roots stimuli thigmotropism tropism Any changes in an environment that cause organisms to respond are considered (1.). A plant s (2.) to stimuli could be slow or rapid, but all plants respond to (3.). There are two main types of stimuli: (4.) stimuli and (5.) stimuli. A positive (6.) identifies a plants response that results in growth toward a stimulus. There are three types of tropisms: phototropism, (7.), and (8.). Another type of response, (9.), describes a plant s response to hours of darkness. This response is seen in flowering plants. Carnations, for example, are (10.) plants, and roses are (11.) plants. Chemicals produced by the plant, called (12.), are also called messengers because they are produced at one part of the plant and affect another part. Four examples of plant hormones are (13.), (14.), (15.), and cytokinins. (16.) assist a plant s response to light, and (17.) help fruit ripen. Plants produce many different hormones. Often two or more hormones (18.). Scientists study the interaction of hormones to find ways to make plants more (19.). Larger plants, faster ripening fruit, and stronger and longer (20.) are just a few of the changes brought about by applying additional hormones to plants. Plant Processes and Reproduction 31

Math Skills LESSON 2 Use Percentages Percentages are used to compare a partial amount to a whole amount. A whole amount is equal to 100%. To calculate percentage, multiply a ratio by 100 and add the percent sign (%). For example, 1 is equal to 0.25, which is 25%. 4 To calculate percentage change, first subtract the final amount from the original amount. Then divide by the original amount and convert to a percentage. A plant grows 1 mm per day when given pure water. When given water with gibberellins added, the plant grows 4 mm per day. What is the percentage increase in growth? Step 1 Subtract the original value from the final value. 4 mm - 1 mm = 3 mm Step 2 Then set up a ratio. Divide the result of Step 1 by the original amount. 3 mm 1 mm = 3 mm Step 3 Multiply by 100 and add a percent sign. 3 100 = 300% Practice 1. A plant grows 3 mm per day when given pure water. When given water with gibberellins added, the plant grows 4 mm per day. What is the percentage increase in growth? 2. A plant grows 5 mm per day when given pure water. When given water with gibberellins added, the plant grows 10 mm per day. What is the percentage increase in growth? 3. Without chemical stimulus, sunflower seedlings grew to 6 cm in 3 days. With chemical stimulus, sunflower seedlings grew to 10 cm in 3 days. What was the percentage increase in growth? 4. Without chemical stimulus, pea seedlings grew to 1.2 cm in 1 day. With chemical stimulus, pea seedlings grew to 2.3 cm in 1 day. What was the percentage increase in growth? 32 Plant Processes and Reproduction

School to Home LESSON 2 Plant Responses Directions: Use your textbook to complete the table. Plant Stimulus Description of Response 1. Auxin a. b. Environmental Stimulus or Chemical Stimulus 2. Cytokinins a. b. 3. Ethylene a. b. 4. Gibberellins a. b. 5. Gravitropism a. b. 6. Photoperiodism a. b. 7. Phototropism a. b. 8. Thigmotropism a. b. Plant Processes and Reproduction 33

Key Concept Builder LESSON 2 Plant Responses Key Concept How do plants respond to environmental stimuli? Directions: On each blank, write the term or phrase that correctly completes each sentence. 1. Changes in the environment that cause an organism to respond are called. 2. Environmental stimuli include,, and. 3. When a response results in plant growth toward or away from a stimulus, the response is called a(n). 4. A(n) tropism occurs when the growth is toward the stimulus. 5. Growth of a plant toward or away from light is called. 6. is a plant s response to gravity. 7. Another response,, describes a plant s response to touch. 8. Vines that coil around a nearby plant are demonstrating. 9. Flowering plants show a response to darkness called. 10. A short-day plant must have more than hours of darkness to flower. 11. A(n) plant does not seem to be affected by the number of hours of darkness. 12. Plants that flower in early summer but not in late fall are called plants. 13. Stems grow away from gravity, and roots grow toward gravity. This describes. 14. A stem grows even when there is no light. 15. Roots growing away from a source of light are examples of tropism. 16. Leaves tend to grow in the direction of. 17. The dropping of leaves in the fall is the tree s response to stimuli. 18. The tendrils of vines coil as a response to. 34 Plant Processes and Reproduction

Key Concept Builder LESSON 2 Plant Responses Key Concept How do plants respond to environmental stimuli? Directions: Answer each question in the space provided. Environmental Stimuli This is the cause. 1. Sunlight enters a room and shines on a potted plant near the window. 2. A seed lands on the soil and starts to grow. 1. 2. What is the effect? What is this response called? 3. The tendril of a vine touches the branch of a nearby shrub. 3. 4. Day-neutral plants reach maturity, and environmental conditions are right. 5. Short-day plants receive less than 12 hours of darkness. 6. A potted plant falls on its side and goes unnoticed. 7. A plant that leans toward the window is moved outside. 8. A fly lands inside the leaves of a Venus flytrap. 9. The roots of a plant are pulled out of the wet soil and left to lay on the ground. 4. 5. 6. 7. 8. 9. 10. A vine touches the side of a building. 10. Plant Processes and Reproduction 35

Key Concept Builder LESSON 2 Plant Responses Key Concept How do plants respond to chemical stimuli? Directions: Label the diagram by writing the three responses plants have to each plant hormone. 1. Auxins 2. Ethylene 3. Gibberellins 4. Cytokinins Directions: Answer the question on the lines provided. 5. Why are plant hormones called messengers? 36 Plant Processes and Reproduction

Key Concept Builder LESSON 2 Plant Responses Key Concept How do plants respond to chemical stimuli? Directions: Respond to each statement in the space provided. List four plant hormones. Explain how the plant responds to the plant hormone. Describe how the response benefits the plant. 1. Summarize how plant hormones benefit plants. 2. Explain three ways you are dependent on plants. 3. Describe how humans use plant hormones to make plants more productive. Plant Processes and Reproduction 37

Enrichment LESSON 2 Forcing Flowers A plant s response to changes in the length of days and nights is called photoperiodism. A plant that blooms only in the summer is a long-day, short-night plant because in summer, in temperate zones, the days are longest and the nights are shortest of any other season. Carnations, chrysanthemums, and poinsettias are available all year long. There are basically two ways that professional flower growers manipulate flowering in plants controlled-light environments and genetic engineering. match could cause the plants to fail to bloom and could cost the grower an entire season s crop. Long-day plants are grown in similar, but warmed environments to induce them to bloom in winter, but they are treated to short periods of light during the night hours. Flashes of light are enough to fool the plant into responding as if it were having a long day. By understanding photoperiodism and controlling periods of light, flower growers keep out-of-season flowers ready to buy at any time. Controlled-Light Environments A short-day plant, such as a chrysanthemum or mum for short, are so-called because when days are short, nights are long, and it is really the long night that is critical. Mums have a critical night length for flowering from between 14 to 16 hours. Professional growers house these plants in vast greenhouses in row after row. To lengthen the night and simulate the mums natural blooming time, the houses are cooled to approximately 20 C (68 F) and are sealed from any light from afternoon to the next morning. No one is allowed in or out without night-vision goggles, and they must enter an anteroom and close the door before they enter the greenhouse. Even striking a Applying Critical-Thinking Skills Directions: Respond to each statement. Genetic Engineering Some researchers are investigating a specific gene that controls flowering periods. Introducing a certain gene to a plant s leaves can cause it to flower at a time when it normally would not. The implication of this kind of genetic manipulation is that plants would not be dependent upon seasonal changes in night length to reproduce. Flower growers would not need expensive greenhouses to force blooms out of season. Benefits to farmers and the world s food supply are enormous. The growing season for food crops with photoperiods, such as spinach, rice, and strawberries could be expanded to most of the year. 1. Explain a benefit of having certain popular flowers available all year long. 2. Infer what effect expanding a crop s growing season would have on the world s food supplies. 3. Describe two very different ways that certain plants can be manipulated to produce out-of-season flowers. 38 Plant Processes and Reproduction

Challenge LESSON 2 Plant Growth Manipulation Below is a list of common plant hormones and their typical functions. Plant Hormone and Typical Function Hormone Auxins Ethylene Gibberellins Function promotes cell growth, root formation on stem and leaf cuttings, stem tip growth dominance, suppression of lateral buds, and increased number of fruits; concentrated in stem tips and young leaves promotes ripening of fruit, flowering in some tropical fruits, and dropping of leaves; concentrated in fruits, flowers, leaves, and roots promotes elongation growth, germination, seedling growth, increased size of fruit, and flowering; concentrated in immature seeds; found in all parts of a plant Apply Knowledge to New Situations Suppose you are a horticulturist who needs to produce certain effects in some plants you want to sell. Examine the table of hormones and their typical effects to help determine your course of action in each situation below. Draw pictures as needed to explain. Situation Answer to Question Drawing 1. You have requests from buyers for a plant that can be grown only from leaf cuttings. You can sell the plants if they are fully rooted and potted for the new customers. What can you do to speed up the development of roots in your leaf cuttings? 2. A pear tree you ordered for your plant nursery won t sell because the fruits are so small. What can you do to assist this tree in producing large, robust fruit? Plant Processes and Reproduction 39

Skill Practice Manipulate Variables LESSON 2: 20 minutes What happens to seeds if you change the intensity of light? Seeds require light, water, gases, and soil to germinate, grow into seedlings, and then grow into mature plants. Different types of seeds require different amounts of each of these factors. What happens if one of these factors is out of balance? Materials plastic tub potting soil fast-growing grass seeds sun shields light source metric ruler mister bottle with water Safety Learn It In any experiment, it is important to keep everything the same except for the item you are testing. The one factor you change, or manipulate, is called the independent variable. Your experiment should also have a control. The control is an individual instance or experimental subject for which the independent variable is not changed. Try It 1. Read and complete a lab safety form. 2. Fill the plastic tub with potting soil. Water the soil and then add more soil. Level it to about 1 2 cm from the top. Spread the grass seeds evenly across the soil. Cover the seeds with a thin layer of soil. 3. Obtain the precut shields of vellum, plastic needlepoint grid, and cardboard. These will be used to change the intensity of light shining on the soil. 4. Cover the soil with the shields by laying them next to each other. Leave one section of soil uncovered. 5. Place the tub on a windowsill or under a growing light. 6. Keep the soil damp, not wet, with a mister. Water gently so the seeds stay in position. 7. Design a table to record observations in the Data and Observations section at the top of the next page. Include columns for day, growth pattern, height, and random sampling counts. Begin observations when seedlings first emerge. Observe seedlings for 3 5 days. 40 Plant Processes and Reproduction

Skill Practice continued Data and Observations Apply It 8. Identify the variables and the controls used in this investigation. 9. Analyze the data you collected through your observations. Which light intensity appeared to bring about the fullest, tallest growth? 10. Draw Conclusions What would happen if you put one section of seeds in total darkness? Would it germinate? If you changed the light intensity immediately after the seeds germinated, would it survive? 11. Key Concept Does the amount of light affect the germination and growth of grass seeds? Explain. Plant Processes and Reproduction 41